1. Field of the Invention
The present invention relates to a photoelectric conversion device, more particularly, a photoelectric conversion device which is formed by using a thin film semiconductor element and a method for manufacturing the photoelectric conversion device. In addition, the present invention relates to an electronic device using a photoelectric conversion device.
2. Description of the Related Art
A number of photoelectric conversion devices generally used for detecting an electromagnetic wave are known, and for example, a photoelectric conversion device having sensitivity in ultra-violet rays to infrared rays are referred to as a photo-sensor in general. A photo-sensor having sensitivity in a visible radiation region with a wave length of 400 nm to 700 nm is particularly referred to as a photo-sensor for visible light, and a number of photo-sensors for visible light are used for devices which need an illuminance adjustment or on/off control depending on a human living environment.
In particular, in a display device, brightness in the periphery of the display device is detected to adjust display luminance. It is because unnecessary electric-power can be reduced by detecting peripheral brightness and obtaining appropriate display luminance. Specifically, such a photo-sensor for adjusting luminance is used for a cellular phone or a personal computer (for example, refer to the Patent Document 1).
In addition, as well as peripheral brightness, luminance of back light of a display device, particularly, a liquid crystal display device is also detected by a photo-sensor to adjust luminance of a display screen (for example, refer to the Patent Documents 2 and 3).
Further, in a display device using a projector, the convergence adjustment is conducted by using a photo-sensor. The convergence adjustment is to adjust an image so that an image of each color of RGB does not generate discrepancy. By using a photo-sensor, a location of an image of each color is detected, and the image is arranged in the right location (for example, refer to the Patent Document 4).
FIG. 6 shows a structure of a photo-sensor that has been used conventionally. In FIG. 6, a first transparent electrode 1002 is formed over a substrate 1001, and a p-type semiconductor layer 1003, an intrinsic semiconductor layer 1004 and an n-type semiconductor layer 1005, which serve as a photoelectric conversion layer, are formed over the first transparent electrode 1002. Further, a second transparent electrode 1006 is formed over the n-type semiconductor layer 1005. Then, a discrete insulating layer 1007 is formed to cover the transparent electrodes 1002 and 1006, and contact holes are formed in the discrete insulating layer 1007. Moreover, a first extraction electrode 1008 connected to the first transparent electrode 1002 and a second extraction electrode 1009 connected to the second transparent electrode 1006 are formed.
In the photo-sensor shown in FIG. 6, since the transparent electrodes 1002 and 1006 are formed, there is a problem that resistance is lowered, static electricity is discharged faster, and electrostatic discharge damage is likely to be caused. In addition, an electric field is concentrated on end portions of the p-type semiconductor layer 1003, the intrinsic semiconductor layer 1004 and the n-type semiconductor layer 1005, which are the photoelectric conversion layer, so that there is a concern that electrostatic discharge damage is more likely to be caused.
Further, since the transparent electrode 1006 is formed over the entire surface of the n-type semiconductor layer 1005 which is an upper layer of the photoelectric conversion layer, and the transparent electrode 1006 is formed over the entire surface of the p-type semiconductor layer 1003 which is a lower layer of the photoelectric conversion layer, intensity of light that is incident to the photoelectric conversion layer can be decreased.    [Patent Document 1] Japanese Patent Laid-Open No. 2003-60744    [Patent Document 2] Japanese Patent No. 3171808    [Patent Document 3] Japanese Patent No. 3193315    [Patent Document 4] Japanese Patent Laid-Open No. 2003-47017